On immigration, a freshman speaks for the right flank of the House GOP.

HC-5, a drab, wood-paneled conference room in the Capitol basement, was quiet last Wednesday as Paul Ryan pushed for immigration reform. All eyes were on the Wisconsin Republican as he touted the economic benefits of bringing illegal immigrants into the work force. He assured his colleagues, who were clustered in cliques — moderates here, old bulls there — that stronger border security remains the leadership’s priority.

As Ryan spoke, freshman Tom Cotton of Arkansas, who was behind him in line, listened carefully. He was calm and upright, and unlike a handful of conservative rabble-rousers in the back, he didn’t sigh as Ryan made his points. Instead, he clasped his hands and focused on his coming speech. After Ryan stepped away, Cotton, a 36-year-old former Army officer, moved forward, and soon his clipped drawl filled the room.

The crowd of 200-plus Republicans took notice. From the start, Cotton’s message was a contrast with Ryan’s. He sliced into the Senate’s immigration bill and dismissed the idea of a compromise. He urged Republicans to oppose a conference with the Senate, and warned that any formal negotiations with the upper chamber would lead to disaster. He then turned to Speaker John Boehner, who was standing nearby, and advised him to tread carefully. For a moment, they engaged in a terse back-and-forth.

“We are not worlds apart from the Senate, we are galaxies apart,” Cotton told the speaker. Boehner responded that Cotton shouldn’t worry. “We’re not going to conference until we’re ready,” he said. The speaker coolly explained to Cotton that it’s important to pass legislation that reflects the position of House Republicans.

Looking on, Steve King of Iowa, long a member of the House’s anti-amnesty forces, smiled. He glanced at his friends, who smiled back. This rookie backbencher, a Harvard Law graduate, was good. “It’s so clear that he’s done the research and taken the time to understand the issue,” King tells me. “He’s also resilient, and not easily discouraged by people who disagree. Usually, you don’t see freshmen get too far out front, but he’s emerging, sooner rather than later, as a leader in this Congress.”

Conservative power brokers agree. Behind the scenes, they’re encouraging Cotton, at the eleventh hour of the immigration debate, to be King’s fresh-faced ally. Cotton’s friends say Republican consultants and movement figures, from talk-radio hosts to think-tank fellows, are constantly e-mailing and calling. They see Cotton not just as a partner but as the last, best hope for a wing of the party often dismissed as senescent.

“He’s certainly an Army ranger I wouldn’t want to mess with,” says Jeb Hensarling of Texas, the chairman of the Financial Services committee. “And in a very short time, he has made his mark. To a lot of senior members, he commands their respect.”

Cotton’s remarks at the closed-door meeting were only the beginning of his efforts. A day later, he published an essay in the Wall Street Journal, where he counseled Republicans to not hand any immigration legislation “off to a conference committee.” The House, he argued, should not go near a bill that includes a path to legalization. He also shrugged off the supposed pressure on Republicans to pass something.

Look for Cotton to continue to fight for a conservative, border-security-centric approach to immigration in the coming weeks. As Boehner and pro-reform heavyweights such as Ryan work to pass a series of piecemeal immigration bills, Cotton, King, and others will question whether that strategy makes sense. They’ll wonder aloud, on the House floor and on the airwaves — Cotton is a favorite of producers for Sunday morning talk shows — whether the GOP is walking into a trap set by the Senate’s Gang of Eight.

Cotton’s rapid ascent as a charismatic, brainy voice for Steve King’s coalition has surprised several leadership staffers, who had planned for months to use Ryan, one of the chamber’s more popular conservatives, as a means of wooing the right flank toward a modified path to legalization. They didn’t think a mostly unknown freshman would be competing with Ryan for the spotlight, both inside and outside the Capitol. Now, with Cotton regularly slamming immigration reform with the poise of Bill Clinton but the politics of Rush Limbaugh, their calculus has changed.

In an interview at his cramped House office on the fourth floor of the Cannon building — freshmen don’t get spacious facilities — Cotton plays down his role as a Paul Ryan–type leader of the conservative bloc. But he is eager to battle any attempt, however well intentioned, to bring forth legislation that’s not entirely enforcement-based.

“There is widespread resistance to legalization, because logic and history say that you will have the legalization and not the enforcement,” Cotton says. “We shouldn’t even be spending this much time on immigration. This is very much an inside-the-Beltway, elite-driven issue, where elites in both parties are aligned.” Cotton adds that out of the more than 1,800 letters and calls his office has received, only a dozen have expressed support for the Senate’s bill. “That’s south of 1 percent,” he says.

“I’m going to keep trying to do what I tried to do at the conference meeting, which was to persuade my colleagues on my view of the facts behind the Senate bill,” Cotton tells me. “I want to try to make the case broadly to the policy community, to the American people, of what I think is the right policy.” He acknowledges that he’s huddling with a variety of off-the-Hill leaders but reiterates that his constituents are fueling his increased cloakroom lobbying and his flurry of television appearances.

A Senate run is another motivating factor, according to Republican insiders who know him well. Cotton and his political team are plotting a potential race next year against incumbent Democrat Mark Pryor. There have held meetings with donors in Washington, D.C., and held informal strategy sessions in Dardanelle, Ark., Cotton’s hometown. Cotton’s confidants think Pryor is vulnerable, especially since he voted aye on the Senate’s immigration bill. But as an amiable, pro-gun Democrat, he’ll be tough to beat, and Cotton isn’t expected to make a final decision until later this year.

Fellow Republicans talk about Cotton as a senator in waiting. “There’s a little jealousy among some of us sophomores who see Tom rising like some kind of perfect-résumé rocket,” says a House Republican from the class of 2010. “But he’s generally pretty low key, and he’s a lot different than Steve [King] and Dana [Rohrabacher of California], the guys I associate with the war against amnesty.” Adds a senior House Republican: “He’s got the smarts and that farmer charm, which can take you far here.”

“You’ve got to take him seriously,” says Tom Cole of Oklahoma, a member of Boehner’s inner circle. “People are listening to what he has to say about how the Senate bill gives way too much power to the executive branch. He’s rightfully concerned about whether the administration would even enforce our border-security bills.”

Cole says Cotton’s leadership qualities are what set him apart, and lend his contribution to the debate a kind of weight within the Republican conference that’s hard to quantify. He says many members share Cotton’s position, and they echo his rhetoric, but it’s rare to see someone “come at this issue with the precision and heart of a man who served in the 101st Airborne, or with his ability to make an argument.”

Cotton’s Journal article showcased that ability. He detailed how “effective enforcement” doesn’t require triggers within a bloated bipartisan bill, but stand-alone bills committed to expanding and improving the border fence, creating a visa-tracking system, and building a “workable employment-verification system.” He used history — specifically Ronald Reagan’s controversial immigration law from 1986 — to demonstrate how comprehensive reform is so routinely full of promises easily forgotten.

Boehner and his advisers are paying attention, and Cole says he expects Cotton to be consulted more as the various immigration bills are considered. King predicts that Cotton could be one of the reasons that a path to legalization dies in the House — the conservative who gave the critics the boost they needed this summer. “The issue is the conference as much as the bills, and he pinpoints that,” King says.

But Cotton’s influence, for the time being, does not extend far beyond the insular world of House conservatives. Some of the top players hardly know him. “Who?” asks Democrat Luis Gutiérrez of Illinois, a leading member of the House’s working group on immigration, when I mention Cotton. He says he doesn’t follow internal Republican dynamics. “I don’t even know what state he’s from,” he says.